MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY
NOVEMBER, 2000
(For general comments about the nature of these summaries, as well as
information on how to download the tabular cyclone track files, see
the Author's Note at the end of this summary.)
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NOVEMBER HIGHLIGHTS
--> Late-season Eastern Pacific tropical storm makes landfall in Mexico
--> Philippines affected by typhoon and tropical storm
--> Southern India struck by tropical cyclone
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***** Feature of the Month for November *****
ATLANTIC SUBTROPICAL SYSTEMS OF 2000
(Part 2)
------------------------------------
This is Part 2 of a three-part feature detailing cyclonic systems
of 2000 in the Atlantic which were either subtropical storms or
depressions or else exhibited some of the features of subtropical
cyclones. The information presented below is taken from material
supplied by David Roth of HPC. Please refer to Part 1 in the October
summary for more background information and some explanations and
caveats.
This month's feature looks at some of the named tropical cyclones of
2000 which, in David's opinion, exhibited some subtropical features
at some point during their histories. For three of these systems
(Florence, Leslie, Michael) official NHC "best tracks" designate some
portion of the respective tracks as either a subtropical depression
or subtropical storm; for Alberto, Gordon, and Helene they do not.
I am repeating here the table of subtropical/hybrid systems which
David provided. (Numbers in parentheses following the storm
designation refer to explanatory notes below.)
I. Subtropical Depression May 19-25
II. Alberto (1) August 14-16
III. Subtropical Storm (2) August 28-30
IV. Subtropical Depression September 10-11
V. Florence (3) September 10-12
VI. Gordon (1) September 17-18
VII. Helene (1) September 24-25
VIII. Subtropical Storm (2) September 30-October 3
IX. Leslie (3) October 4-8
X. Michael (3) October 14-17
XI. Subtropical Storm (4) October 25-28
(1) The official NHC "best tracks" do not treat any portion of Alberto,
Gordon, or Helene as subtropical. In general, once a tropical
cyclone has been named, NHC treats it as a tropical system through-
out the remainder of its life--both operationally and in post-
analysis--even if at some point it exhibited some subtropical
features.
(2) According to Jack Beven, these two systems possibly could qualify
as subtropical storms pending a careful analysis of all the
available data. For the time being they should be regarded as
possible subtropical storms.
(3) Subtropical portions of the tracks of Florence, Leslie, and Michael
are designated in the "best tracks" for these cyclones. The dates
of their subtropical phases, however, might not necessarily agree
with those David has assigned above.
(4) This storm has already been officially recognized as a subtropical
storm by TPC/NHC.
Since Hurricane Florence, Tropical Storm Leslie, and Hurricane
Michael have already been covered in the monthly summaries, and the
official storm reports are available on TPC/NHC's website, these
storms will not be mentioned further here. Regarding Alberto,
Gordon, and Helene, it should be understood that officially, in
post-seasonal analysis, TPC/NHC did not designate any portion of the
tracks of these cyclones as subtropical storms. However, all three
of them did exhibit, at some point in their lives , a few of the
features which often characterize subtropical cyclones. Following a
practice dating back to the early years of working with subtropical
systems (e.g., Tropical Storm Gilda of October, 1973), if an already-
named tropical cyclone transforms into a subtropical cyclone and merits
public advisories, the system will continue to be treated operationally
as a tropical cyclone. In some cases (e.g., Gilda, 1973, and Klaus,
1984), the subtropical portion of the track was so-designated in the
"best track" file; in other cases (e.g., Amy, 1975, and Gordon, 1994)
the "best track" defines the storm as tropical for its entire history.
II. Alberto, August 14-16. Hurricane Alberto had already wandered the
Atlantic for ten days prior to the 14th. On that day the cyclone moved
into 24 C water as it approached the 40th parallel, convection became
shallow, the eye disappeared, and a cold front was swinging around its
western periphery but the cool and dry air had not invaded its
immediate center. This combination of features gave Alberto an
appearance somewhat similar to that of a subtropical storm. Its north-
ward motion was blocked by a slow-moving ridge to its north. On the
15th bands of dry air encircled the center as the system began to loop
back to the south towards warmer waters with an eye-like feature, but
its convection remained shallow. On the 16th bursts of deep convection
developed near the immediate center and the stratocumulus shield on its
western periphery became multicellular, indicative of the warmer waters
it was moving over and an overall warming of its environment. Alberto
regained a true eye late that day with a warming core. The storm was
upgraded to hurricane status (for the third time) and lived several
more days before finally escaping into the westerlies. (NOTE: The
August global summary contains a discussion of Alberto written by
Eric Blake, and the official storm report on the hurricane, authored
by Jack Beven, is available on TPC/NHC's website.)
VI. Gordon, September 17-18. While Gordon was a hurricane in the
southeastern Gulf of Mexico, an upper-level vorticity maximum became
co-located over the surface circulation, totally exposing the surface
center in the first morning visible images on the 17th. However, the
surface winds were slow to decrease and the pressure remained
relatively low until landfall as the system fed off this increase in
baroclinic instability (with slightly colder air aloft) while lurking
over 31 C water; hence, the suggestion that Gordon was at least partly
subtropical. By the 18th it had hooked up with a frontal boundary in
the Southeast, ultimately occluding later that day. That completed
Gordon's transition to an extratropical cyclone. (NOTE: The September
global summary contains a discussion of Gordon, and the official storm
report on the system, authored by Stacy Stewart, is available on
TPC/NHC's website.)
VII. Helene, September 24-25. A tropical storm that made landfall near
Fort Walton Beach, Florida, on the night of the 21st/22nd, Helene
became linked with a cold air wedge (stationary front) by the evening
of the 22nd, transforming the cyclone into an extratropical LOW. As
Helene was moving out to sea near the Outer Banks, it left the frontal
boundary behind and quickly redeveloped into a subtropical cyclone,
embedded within deep southwesterly flow ahead of a frontal system in
New England. Its circulation was elongated northeast/southwest and
convection was limited in its eastern half. As it moved along the Gulf
Stream, it fed off its latent baroclinicity (temperature gradient),
deepening into a 55-kt subtropical storm on the night of the 24th/25th.
Once the system had moved east of Nova Scotia, it moved into colder
waters and frontogenesis occurred with the cyclone quickly occluding
on the 25th. (NOTE: The September global summary contains a discussion
of Helene, and the official report on the storm, co-authored by Lixion
Avila and Eric Blake, is available on TPC/NHC's website. It should be
noted that while during Helene's Atlantic Ocean phase the cyclone was
not exactly a classic tropical storm, the decision was made in post-
storm analysis to treat this portion of the cyclone's history as a
tropical storm.)
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ACTIVITY BY BASINS
ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico
Activity for November: No tropical cyclones
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NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180
Activity for November: 1 tropical storm
NOTE: Much of the information presented below was obtained from the
TPC/NHC discussion bulletins issued with every regular advisory (CPHC
for locations west of 140W.) All references to sustained winds imply
a 1-min averaging period unless otherwise noted.
Northeast Pacific Tropical Activity for November
------------------------------------------------
In the Northeast Pacific basin the month of November averages a
tropical storm or hurricane about once every four years (the exact
average for the Eastern Pacific east of 140W for the period 1971-1999
was 0.28). This year's Tropical Storm Rosa was the first November
cyclone in the NEP basin since Hurricane Rick in 1997. Like Rick,
Rosa moved northeastward and made landfall in southeastern Mexico,
but unlike the former storm, Rosa did not reach hurricane intensity.
The tropical cyclone peaked at 55 kts but had weakened to a minimal
tropical storm by the time of landfall.
The following report on Rosa was written by John Wallace of San
Antonio, Texas. A very special thanks to John for writing the
discussion for me.
Tropical Storm Rosa (TC-19E)
3 - 8 November
-----------------------------
Tropical Storm Rosa was a rare November storm, of which the NEP
averages only 2.8 per decade--less than the Atlantic rate of roughly
4.4 per decade.
Intermittent, strong convection persisted in the southwest Caribbean
through much of the month of October. A tropical disturbance formed
north of Panama beginning on 28 October. Its convection increased, and
hints of cyclonic structure were apparent, resulting in a closed LOW
being depicted on the surface analyses by the evening of the 29th.
The LOW generated strong convection and maintained fair cyclonic
structure as it drifted westward. It weakened substantially early on
the 31st as it crossed the Isthmus of Panama, but the LOW apparently
reconsolidated under a cluster of thunderstorms west of Panama.
The LOW tracked slowly westward under the influence of a mid-level
ridge to its north, and had organized enough to warrant its upgrade to
Tropical Depression Nineteen-E at 2100 UTC on 3 November when it was
located approximately 475 nm southeast of Salina Cruz, Mexico.
The depression was slow to intensify, though SSTs and shear were
most favorable. A report of a 30-kt MSW and 12-foot seas from ship
WMBK, just east of the center at 0000 UTC on the 3rd, justified a
slight increase in the estimated MSW to 30 kts on the second advisory.
For the most part, though, satellite MSW estimates fluctuated between
25 and 30 kts, based on mercurial convective organization and
sometimes conflicting data.
The cyclone's organization finally increased enough to justify its
being upgraded to Tropical Storm Rosa at 1500 UTC on 5 November, though
the forecaster on duty at the time acknowledged that the classification
was dubious. The storm was centered by this time about 350 nm south-
southwest of Salina Cruz. At the same time, Rosa's track, roughly due
west earlier, began to make an expected northwestward turn in response
to a strong mid- to upper-level trough to its west. The tropical
storm's organization increased significantly between its upgrade and
0900 UTC on 6 November, when it reached its estimated peak MSW of
55 kts about 300 nm south-southeast of Acapulco. Around this time the
cyclone's track turned ever more to the north toward the Mexican coast.
As Rosa seemed to flirt with the possibility of reaching hurricane
intensity, at 1500 UTC on 6 November the government of Mexico issued a
hurricane watch for the coast extending from Acapulco to Puerto Angel.
Interestingly, at this time there was speculation from one of the
forecasters that Rosa's MSW might have been as low as 40 kts, based on
Quickscat data that conflicted with Dvorak intensity estimates. Rosa
attained its estimated minimum CP of 993 mb at 2100 UTC on 6 November
which it maintained through the next advisory.
The storm stalled briefly at 0300 UTC on 7 November and began its
recurvature as it turned to the north, then north-northeast. A
tropical storm warning was added to the hurricane watch area at
0900 UTC on the 7th, while the watch/warning zone was extended east to
Salina Cruz at 1500 UTC. Rosa's cloud pattern began to show the
effects of southwesterly shear from the same trough responsible for its
recurvature and a weakening trend began. The hurricane watches were
dropped, while tropical storm warnings were raised for the coast from
Punta Maldonado to Tonal at 1800 UTC on the 7th. A reconnaissance
mission investigated Rosa around 1600 UTC on the 7th; they found a MSW
of 50 knots and a CP of 1000 mb, in excellent agreement with Dvorak
estimates, which also averaged 50 knots. It's worth noting that the
reconnaissance crew also found a closed, 20-nm eyewall; there was no
hint of this in satellite imagery and was unusual for a storm that was
well-below hurricane intensity.
Rosa made landfall on the Mexican coast near Puerto Angel at
0600 UTC on 8 November with a MSW of 40 knots and CP of 1001 mb. Rosa
was only the second November storm since 1971 to make landfall in
Mexico (the other being Hurricane Rick in 1997). Already weakening
when it made landfall, Rosa was quickly obliterated by the rough
terrain. It was downgraded to a depression at 0900 UTC, at which point
all warnings were discontinued. The final advisory was issued at
1500 UTC on 8 November, only nine hours after landfall, with the
dissipating depression's center located inland about 75 km north of
Salina Cruz.
No casualties or significant damage are known from Rosa's landfall;
if any come to light, the information will be reported in a future
summary.
The official storm report on Tropical Storm Rosa, prepared by
Richard Pasch, is available on TPC/NHC's website at the following
URL: http://www.nhc.noaa.gov/2000rosa.html> .
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NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180
Activity for November: 1 tropical depression
1 tropical storm
1 typhoon
NOTE: Most of the information on each cyclone's history presented in
the narrative will be based upon JTWC's advisories, and references to
winds should be understood as a 1-min avg MSW unless otherwise noted.
However, in the accompanying tracking document I have made comparisons
of coordinates with JMA (Japan) and the Philippines (PAGASA) when their
positions differed from JTWC's by usually 40-50 nm or more. A special
thanks to Michael V. Padua, owner of the Typhoon 2000 website, for
sending me the PAGASA and JMA tracks.
In the title line for each storm I plan to reference all the cyclone
names/numbers I have available: JTWC's depression number, the
JMA-assigned name (if any), JMA's tropical storm numeric designator,
and PAGASA's name for systems forming in or passing through their area
of responsibility.
Northwest Pacific Tropical Activity for November
------------------------------------------------
The Republic of the Philippines was the target of both of the named
tropical cyclones forming in the Northwest Pacific basin during
November. Early in the month Typhoon Bebinca/Seniang followed a track
across southern Luzon almost identical to that taken by Typhoon
Xangsane/Reming only a week earlier. And, like the earlier storm,
Bebinca caused a considerable amount of damage and several dozen
fatalities. Late in the month Tropical Storm Rumbia crossed the
southern Philippines and was responsible for a dozen or so fatalities.
Another tropical depression (TD-32W) formed on 8 November roughly
100 nm east-northeast of the northern tip of Luzon. This depression
formed in an environment of southerly vertical shear which prevented
it from strengthening into a tropical storm. The system initially
moved northward, later curving to the northeast. By 1800 UTC on the
8th the shear was increasing and dry air was invading the depression's
central region, indicating that extratropical transition was underway.
The system moved just north of Okinawa around 1200 UTC on 9 November
and by 1800 UTC had become an extratropical LOW about 150 nm east-
northeast of the island.
Finally, as the month opened, Typhoon Xangsane was skirting Taiwan
as it raced northeastward and had transitioned into an extratropical
gale southwest of Japan by 2 November. See the October summary for
the complete report on Typhoon Xangsane.
Typhoon Bebinca (TC-31W / TY 0021 / Seniang)
31 October - 8 November
---------------------------------------------
Bebinca: contributed by Macau, is the name of a Macanese milk pudding
served in the Portuguese restaurants of Macau
The STWO issued by JTWC at 0600 UTC on 28 October mentioned that an
area of convection had formed about 330 nm east of Yap. Synoptic data
indicated a developing LOW within the monsoon trough. The disturbance
migrated to the west but remained poorly organized with multiple
circulation centers evident in the monsoon trough. By the 30th the
area of convection was located about 270 nm southeast of Yap and was
looking healthier. There was an increase in deep convection associated
with cross-equatorial flow south of the LLCC and some isolated deep
convection was developing near the center; therefore, JTWC upgraded the
development potential to Fair. By 2200 UTC the main area of convection
was located near Palau and JTWC issued a Formation Alert as the system
had continued to show signs of development and was located within an
environment favorable for intensification.
By 0000 UTC on 31 October convection had become much better
organized about the LLCC and JTWC initiated warnings on TD-31W. The
center of the depression was located approximately 85 nm northwest of
Palau or about 475 nm east of the Philippine island of Mindanao. Also
at 31/0000 UTC PAGASA began issuing bulletins on the depression, naming
it Seniang. Tropical Depression Seniang was initially moving to the
west-northwest at a fairly good clip (around 15-20 kts), but the
forward motion gradually slowed. PAGASA upgraded Seniang to a tropical
storm at 31/1200 UTC while JTWC maintained the system as a 25-kt
depression through 1800 UTC. The center had been partially-exposed
but by 1800 UTC a convective band was beginning to wrap into the LLCC.
By 0000 UTC on 1 November satellite intensity estimates had reached
35 kts and microwave imagery revealed deep convection organizing over
the LLCC, so JTWC upgraded TD-31W to a tropical storm. At the same
time JMA upgraded the depression to a tropical storm and named it
Bebinca. Bebinca's center was located roughly 230 nm east-northeast
of Surigao on the northern tip of Mindanao.
At the time it was named Tropical Storm Bebinca was moving north-
westward, but the storm's heading changed more to west-northwesterly
with time as it came under the steering influence of the subtropical
ridge to its north. The cyclone's organization continued to improve
and by 1800 UTC the 1-min avg MSW had reached 55 kts with the storm
centered about 115 nm east-southeast of Catanduanes Island. (JMA's
maximum 10-min avg wind estimate was 50 kts while PAGASA's was slightly
higher at 60 kts.) Bebinca exhibited one interesting feature which
Mark Lander pointed out: around 01/1200 UTC the storm blew up a large
Central Cold Cover (CCC) with cloud top temperatures colder than -80 C
and in some limited areas colder than -90 C. At 0000 UTC on the 2nd
the storm's center was located about 40 nm east-southeast of
Catanduanes Island and moving west-northwestward at 12 kts. PAGASA
upgraded Bebinca/Seniang to a 65-kt typhoon at this juncture, but JTWC
did not upgrade the storm to typhoon status until 0600 UTC. A SSM/I
pass at 01/2137 UTC revealed a developing eye and animated water
vapor imagery depicted improved single-channel outflow south of the
system.
The center of Bebinca/Seniang apparently passed over or just north
of Catanduanes around 0300 UTC--at 0600 UTC it was centered about
50 nm northwest of the island or about 45 nm north-northeast of Naga
City (where my associate Michael Padua lives). JTWC upgraded Bebinca
at 0600 UTC to a typhoon with the MSW estimated at 75 kts. (PAGASA
reported the maximum 10-min avg wind at 70 kts while JMA was lower at
55 kts.) Animated visible imagery had depicted rapid intensification
during the previous six hours with a well-developed primary spiral
convective band developing over the northern semicircle and contracting
around the vortex center. By 1200 UTC on 2 November Bebinca/Seniang's
center was located about 65 nm northwest of Naga City or 90 nm east
of Manila--just off the coast of Luzon. JTWC upped the MSW estimate
to 85 kts while JMA upgraded the storm to a 65-kt (10-min avg) typhoon.
A recent observation from Daet (which would have been a short distance
south of the cyclone's center) indicated sustained 1-min avg winds of
43 kts with a SLP of 994.5 mb. Outflow was impressive in all quadrants
and enhanced infrared imagery revealed a small, cloud-filled eye.
The observation from Daet in the preceding paragraph was the only
synoptic observation given in any JTWC warning as the typhoon was about
to make landfall. Michael Padua of Naga City (13.6N, 123.2E) made
hourly observations with his instrumentation during the approach and
passage of Bebinca/Seniang. The lowest pressure Michael recorded was
994.6 mb at 02/0700 UTC while the highest 1-min avg MSW of 30 kts from
the southwest occurred at 02/0900 UTC when the typhoon's center was
46 nm north-northwest of his site. A peak gust of 39 kts was recorded
at 0934 UTC. Also, at 0900 UTC, Daet reported a peak gust of 65 kts
with an attendant pressure reading of 986.7 mb. At PAGASA's Bicol
River Basin Flood Forecasting Center near Camaligan, 235 mm of rain was
recorded in the 48 hours ending at 02/0000 UTC. More information can
be found at: http://www.geocities.com/taifun00/bebinca_obs.htm> .
The eye of Typhoon Bebinca/Seniang apparently made landfall along
the east coast of Luzon shortly before 1800 UTC at a point about 39 nm
(72 km) east of Manila at its peak intensity (per JTWC) of 90 kts.
The storm moved westward across a narrow part of Luzon island, passing
just south of Manila and across Manila Bay, and by 03/0000 UTC was
beginning to emerge into the South China Sea at a point about 33 nm
(61 km) slightly south of due west of Manila. JMA had by this time
downgraded Bebinca to a 55-kt tropical storm, but JTWC still maintained
the MSW at 90 kts based on current satellite intensity estimates.
Convection had rapidly weakened but some new central convection was
redeveloping southwest of the LLCC. By 0600 UTC the cyclone's center
was over water about 85 nm west of Manila. Deep convection had
weakened significantly during the previous six hours due to interaction
with Luzon, especially in the northern semicircle. JMA downgraded
Bebinca to a 45-kt tropical storm while PAGASA and JTWC still main-
tained the storm as a typhoon. JTWC's 1-min avg MSW estimate was
80 kts, but the remarks in the warning indicated that this was based
on satellite intensity estimates ranging from 55 to 90 kts.
It seems likely that JMA's lower intensity estimate was probably
more on target as JTWC abruptly dropped the MSW to 55 kts on the next
warning. (PAGASA kept Bebinca/Seniang at 65-kts until 1800 UTC.)
Most of the remaining convection had decoupled from the LLCC and
was located to the east along the windward side of the Zambales
Mountain range. As Bebinca began to move northwestward and gradually
pulled away from the Luzon landmass, convection began to redevelop near
the LLCC. The system was under good diffluence with weak to moderate
vertical shear and was forecast to intensify for a couple of days
until it began to encounter stronger shear to the north. Throughout
4 November and into the 5th, JTWC and JMA held their respective MSW
estimates at 55 kts while PAGASA's 10-min avg MSW was 60 kts. The
storm had moved out of Manila's AOR by 05/0000 UTC. Bebinca became
quasi-stationary around 0000 UTC about 200 nm west-northwest of
Lincayen in the Philippines. A 04/2219 UTC microwave image showed
what appeared to be a banding eye, but within 30 minutes the convection
had weakened and the eye had filled.
By 05/0600 UTC Bebinca had begun a slow northward trek west of
Luzon with convection still pulsing near the center. Based on Dvorak
intensity estimates of 65 kts, JTWC upgraded Bebinca once more to
typhoon status at 1200 UTC when it was centered approximately 275 nm
southeast of Hong Kong. (JMA concurrently upped their 10-min avg
sustained wind estimate to 60 kts, but never reclassified Bebinca as
a typhoon.) Outflow over the system was good, but upper-level winds
were continually advecting the convection to the northeast. Cloud
tops were beginning to warm by 06/0000 UTC but convection was still
well-organized around the center. However, twelve hours later animated
satellite imagery indicated that the convection was rapidly dissipating
while the northeastern quadrant was being sheared to the northeast.
JTWC downgraded Bebinca to a 45-kt tropical storm at 1200 UTC on the
6th with the center approximately 190 nm southeast of Hong Kong.
Further reduction to minimal tropical storm intensity took place
at 1800 UTC, and Bebinca was downgraded to a depression at 0000 UTC
on the 7th. The LLCC was fully-exposed with well-defined low-level
cumulus cloud lines to the south of the center. The decaying storm
had been tracking generally northward into a weakness in the sub-
tropical ridge, but a strengthening low-level ridge turned Bebinca
westward during its final depression stage. Some occasional minor
bursts of convection were noted, but the system continued to wind
down. JTWC issued the final warning at 08/0000 UTC, placing the
poorly-defined and convection-free LLCC about 80 nm southwest of
Hong Kong, just off the southern Chinese coast.
Like Xangsane/Reming a week earlier, Typhoon Bebinca/Seniang left
a trail of death and destruction across Luzon. The highest death toll
noted by the author was 43 with nine persons reported missing. Of the
43 fatalities, 22 died in landslides, 14 drowned, four died when a
concrete wall collapsed on them in Calamba, Laguna, and the others died
when they were hit by flying objects. Floodwaters inundated portions
of the metropolitan Manila area, forcing 630,000 persons to flee their
homes. Government offices, schools and financial markets closed, all
airline flights from the capital were cancelled, and power blackouts
occurred in much of the city.
Tropical Storm Rumbia (TC-33W / STS 0022 / Toyang)
27 November - 8 December
---------------------------------------------------
Rumbia: contributed by Malaysia, is the name of a type of palm tree
which yields sago. The tree commonly grows along riverbanks,
in swampy areas, or in areas near water.
The first "rumblings" of Rumbia can be traced to an area of
convection which developed around 25 November very deep in the tropics
about 450 nm southeast of Palau. A weak LLCC was present with some
convection to the north, and the disturbance was located beneath light
diffluent flow. Over the next couple of days the disturbance moved
westward and by 27/0600 UTC was located about 80 nm east of Palau.
JTWC upgraded the development potential to Fair, but PAGASA had begun
issuing bulletins on the system at 0000 UTC, naming it Tropical
Depression Toyang, and by 0600 UTC had already upgraded it to a
tropical storm. JMA classified the system as a tropical depression
at 1800 UTC, and JTWC issued a Formation Alert at 1900 UTC. A recent
QuikScat pass had shown a LLCC embedded in the monsoon trough with
10-15 kt winds near the center but stronger winds in the gradient
flow along the periphery.
JTWC initiated warnings on the system as TD-33W at 0000 UTC on the
28th with the center estimated to be about 400 nm east of Mindanao.
The remarks indicated that QuikScat data showed 20-25 kt winds near the
center with stronger winds along the northern periphery. The MSW for
the first warning was reported as 30 kts. This implies that the system
still had significant monsoon depression characteristics. The author
has noted that often with these larger systems originating in the
monsoon trough PAGASA is ahead of JTWC and JMA in initiating warnings
and upgrading to tropical storm status. Perhaps it is because of the
great potential for disastrous flooding such systems may pose that
PAGASA does not draw such a fine distinction between monsoon and
"tropical" depressions/storms. JMA upgraded 33W/Toyang to a tropical
storm at 0600 UTC, naming it Rumbia, and JTWC followed suit six hours
later. Dvorak intensity estimates had reached 35 kts, although the
stronger winds were still located in the gradient flow to the north.
At 1800 UTC JTWC abruptly increased the MSW estimate to 50 kts as
convection had continued to intensify and organize around the LLCC.
Interestingly, the satellite intensity estimates upon which the MSW
was based were 35 and 45 kts. Rumbia was centered at this time about
325 nm east-southeast of Surigao on the northern tip of Mindanao.
The storm was moving slowly in a general westerly direction,
occasionally jogging to the southwest or remaining quasi-stationary.
Throughout 29 November Tropical Storm Rumbia/Toyang maintained its
intensity of 50 kts (45 kts 10-min avg) in the face of moderate
easterly vertical shear which kept the deeper convection sheared to
the western half of the storm. JTWC and PAGASA both increased their
respective estimated MSWs to 55 kts at 30/0000 UTC as the convection
had increased in areal extent. The center of Rumbia/Toyang was then
located approximately 130 nm east of the city of Surigao and moving
west-northwestward at 11 kts. Multi-spectral imagery around 0600 UTC
depicted low-level cumulus cloud lines east of the deep convection;
therefore, the LLCC was estimated to be beneath the eastern edge of
the convection.
Tropical Storm Rumbia/Toyang reached the vicinity of the small
island of Siargao (just off northeastern Mindanao) around 1200 UTC
on 30 November at its peak estimated intensity of 55 kts. The exact
path of the storm as it moved through the southern Philippines is a
little uncertain. PAGASA's and JTWC's positions were in fairly good
agreement, and using JTWC's synoptic-hour coordinates, the center of
Rumbia/Toyang moved from near Siargao northwestward and was located
in the Leyte Gulf around 30/1800 UTC. By 0000 UTC on 1 December the
center had crossed Leyte and was near San Isidro on extreme north-
western Leyte. The cyclone then seemed to cross Masbate and tiny
Tablas islands, and by 01/1200 UTC had reached the Tablas Strait just
east of Mindoro where it remained quasi-stationary for several hours.
However, at 0000 UTC on the 2nd JTWC relocated the storm's center
well to the south of the previous warning position--south of Mindoro
and west of Panay, so the actual track taken by Rumbia's center may
have been to the south of that described above, possibly crossing
Panay Island and even the northern portions of the islands of Cebu
and Negros.
The JTWC warning at 30/1800 UTC noted that the storm displayed a
large, asymmetric cloud shield about 360 nm in diameter and that the
LLCC was near the eastern edge of the deep convection about 45 nm into
the cloud shield. The MSW was still maintained at 55 kts--the remarks
noted that one satellite intensity estimate of 77 kts had been
received. Rumbia/Toyang gradually weakened as it moved through the
Philippine archipelago. It is interesting to note that PAGASA had
downgraded the storm to a 30-kt depression by 01/0000 UTC while JTWC's
and JMA's MSW estimates were still 50 kts and 40 kts (10-min avg),
respectively. JTWC had reduced the system to a minimal tropical storm
by 1800 UTC, noting that the remaining deep convection was moving
off the coast of Mindoro into the South China Sea. The next JTWC
warning effected the above-mentioned relocation and also downgraded
Rumbia to a tropical depression. The LLCC was very weak and both
visible and microwave imagery revealed multiple circulation centers.
The weakening depression continued to move westward into the South
China Sea. Its diffuseness and difficulty in tracking is evidenced
by the disparity between some of JTWC's and PAGASA's coordinates: the
PAGASA position for 0600 UTC was over 100 nm to the west-northwest of
JTWC's locaiton, and the difference was over 150 nm for the next two
warnings. The 02/1800 UTC bulletin was PAGASA's final one on Toyang.
JTWC continued to issue warnings through 0000 UTC on 4 December as
Rumbia sailed rather quickly westward across the South China Sea. The
03/1800 UTC warning had placed the depression's center about 275 nm
east-southeast of Cam Rahn Bay, Vietnam, but the (temporarily) final
warning at 04/0000 UTC relocated the center to a point approximately
60 nm south-southeast of the previous position--roughly 195 nm west-
northwest of the southwestern tip of Palawan Island. Convection
near the system was sheared 90 nm to the northwest of the LLCC and
the strongest convection was being caused by convergence in the
northeast monsoon. The depression was forecast to track southwestward
and dissipate over water due to increasing cold air entrainment and
increasing vertical shear.
The remnants of Rumbia continued to drift westward across the
South China Sea, and the STWO issued at 05/0600 UTC rated the potential
for redevelopment as Poor. However, the disturbance suddenly re-
intensified and JTWC resumed warnings at 05/1200 UTC, directly
upgrading the system to Tropical Storm Rumbia, based on satellite
intensity estimates of 25 and 35 kts. A SSM/I pass depicted deep
convection confined to the western semicircle of the system. Rumbia
was centered about 450 nm southeast of Da Nang, Vietnam, or roughly
halfway between the Vietnamese coast and northern Borneo. This modest
re-intensification of Rumbia likely happened because the disturbance
had made its way under an upper-level ridge axis. The cyclone was
embedded in a monsoon trough extending eastward from a broad, LLCC
over the southern Bay of Bengal.
The rejuvenated cyclone tracked slowly west-northwestward and north-
westward toward southeastern Vietnam. The center remained partially-
exposed with convection sheared to the west of the LLCC. By 1800 UTC
on 6 December the center had become fully-exposed with convection
sheared 80 nm to the west, so JTWC downgraded Rumbia once more to a
tropical depression. The center was located approximately 200 nm
east-southeast of Ho Chi Minh City, Vietnam, and was tracking slightly
south of due west. By 07/0000 UTC all satellite intensity estimates
had fallen below 35 kts and the system continued to slowly weaken as
it drifted off the Vietnamese coast. No convection remained near the
LLCC after around 1200 UTC and JTWC issued the final warning at 1800
UTC with the weak center near the extreme southern tip of Vietnam.
Press reports indicated that 12 persons lost their lives in the
Philippines due to Rumbia/Toyang with seven people missing. One
report mentioned winds of 74 kts--the source of this report was not
given. If the report is valid, the 74 kts likely represents peak
gusts. There is no indication that Rumbia reached typhoon intensity,
but gusts of 74 kts could reasonably be expected with a 55-kt MSW.
Nine towns were flooded in northern Mindanao, and two days after the
storm, more than 4100 individuals remained in temporary shelters while
more than 1700 homes and several bridges were damaged or destroyed by
the flooding and landslides.
After writing the bulk of this report, I discovered in my files some
e-mail from Mark Lander I'd saved which is interesting. Mark reported
that, like Bebinca a few weeks earlier, Rumbia had blown a Central Cold
Cover (CCC) with extremely cold cloud tops. For a period of several
hours on 28 November (based on replacement tables on METSAT processing
equipment) the coldest pixels in the image yielded temperatures of
-97.2 C. At 1100 UTC two pixels yielded a temperature of -100.9 C.
This is very close to the record of -102 C reported by Ebert and
Holland in an analysis of Tropical Cyclone Hilda near Australia in
1990. According to Mark, some typical characteristics of CCCs, at
least in the NWP basin, are: (1) they usually begin to form at local
sunset, (2) they reach their greatest size and coldest temperatures
near local midnight, and (3) they usually occur in weaker cyclones
in the 45-65 kt intensity range.
NOTE: I e-mailed Mike Padua and asked him if PAGASA makes any
distinction between monsoon depressions and tropical depressions. Mike
checked with some contacts he has in PAGASA and was told that they do
not use the term "monsoon depression" in any warnings or bulletins.
Some such systems are referred to as "active low-pressure areas".
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NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea
Activity for November: 1 tropical cyclone of hurricane intensity
NOTE: The tracking and intensity information for North Indian Ocean
Basin tropical cyclones is based primarily upon operational warnings
from the Joint Typhoon Warning Center of the U. S. Air Force and Navy
(JTWC) at Pearl Harbor, Hawaii. Occasionally some information may
be gleaned from the daily Tropical Weather Outlooks and other bulletins
issued by the Indian Meteorological Department (IMD), which is the
WMO's RSMC for the basin.
The MSW are based on a 1-min averaging period, which is used by
all U. S. civilian and military weather services for tropical cyclone
warnings. For synoptic observations in the North Indian region,
both 10-min and 3-min average winds are employed, but IMD makes no
attempt to modify the Dvorak scale for estimating tropical cyclone
intensity; hence, a 1-min avg MSW is implied. In the North Indian
basin JTWC usually does not initiate warnings until a system is
well-organized and likely to attain tropical storm status within
48 hours.
North Indian Ocean Tropical Activity for November
-------------------------------------------------
The Bay of Bengal produced its third tropical cyclone of the fall
transition season late in November. The system was also the first to
reach hurricane intensity in the NIO basin this year. Tropical
Cyclone 03B made landfall in southeastern India as a minimal hurricane
where it caused some scattered damage. The system weakened while
crossing India but underwent some modest re-intensification in the
Arabian Sea, eventually dissipating several hundred miles east of the
Somalian coast during the first week of December.
Tropical Cyclone (TC-03B)
26 November - 6 December
--------------------------
The beginnings of Tropical Cyclone 03B can be traced to a LLCC which
developed on 25 November approximately 200 nm west of Phuket, Thailand.
A 25/1443 UTC SSM/I pass depicted a fully-exposed LLCC with deep
convection sheared west of the center. The disturbance moved westward
across the Bay of Bengal with convection gradually improving in
organization and increasing in areal extent. JTWC issued a Formation
Alert at 26/0700 UTC with the center of the system estimated to be
about 700 nm east-southeast of Madras, India. Outflow was improving
as the depression moved toward the subtropical ridge axis extending
over the Bay. The maximum winds were estimated at 25-30 kts, so in
the NWP basin the disturbance would likely have been treated as a
tropical depression. (Another tropical disturbance was present at
the same time in the Arabian Sea and had been given a Fair development
potential, but this system failed to develop further.)
JTWC initiated warnings on TC-03B at 1200 UTC on 26 November with
an initial warning intensity of 35 kts. Deep convection had weakened
some during the previous six hours but the system remained well-
organized with deep convection located over the LLCC. The cyclone
was located about 540 nm east of Sri Lanka and was tracking west-
northwestward at 9 kts. Over the next couple of days the system
continued to march to the west-northwest and gradually strengthened.
By 1200 UTC on the 27th the MSW had increased to 45 kts, and a
27/1126 UTC SSM/I pass depicted a primary convective band feature
wrapping in toward the center from the southwest. Microwave imagery
around 28/0000 UTC depicted a well-defined eye feature and the MSW
estimate was increased to 55 kts in the 28/0000 UTC JTWC warning.
The eye feature persisted and at 1200 UTC the MSW was increased to
65 kts, making TC-03B the first cyclone to reach hurricane intensity
in the NIO basin this year. The storm was centered approximately
100 nm southeast of Madras and had turned to a westward course.
University of Wisconsin CIMSS charts indicated moderate vertical shear
continuing over the system. The shear likely was one factor which
prevented the cyclone from intensifying any further beyond minimal
hurricane force. The storm continued moving due westward and
maintained its 65-kt MSW until landfall in India at 1000 UTC on
29 November near Cuddalore, about 30 km south of Pondicherry. The
cyclone weakened quickly over land; by 30/1200 UTC the majority of
the convection had moved offshore into the Arabian Sea and the LLCC
was difficult to locate. The weakening depression continued west-
ward and had moved into the Arabian Sea by 0600 UTC on 1 December.
A few diurnal bursts of convection had been noted north of the LLCC,
but JTWC anticipated that the system would continue to dissipate and
issued the final warning at 0600 UTC.
The STWO issued at 1800 UTC on 2 December indicated that the
remnants of TC-03B were still weak but that outflow was good and the
system had a fair chance of redeveloping. By 0600 UTC on the 3rd
the disturbance had undergone some re-intensification with convection
increasing in all quadrants. JTWC re-initiated warnings on TC-03B,
placing the center about 600 nm southwest of Bombay, India, and moving
westward quickly at 17 kts. The MSW was set at 35 kts, based on
Dvorak intensity estimates of 30 and 45 kts. The system was well-
organized with good outflow aloft. However, the intensification trend
was short-lived--at 1800 UTC the MSW was decreased to 30 kts. The
LLCC remained well-defined but convection had weakened. The cyclone
was tracking west-southwestward across the Arabian Sea and was still
under a favorable upper-level environment, so some modest strengthening
was forecast for the next 12 hours or so before dry air and increasing
vertical shear were expected to begin weakening the system.
However, the cyclone never regained tropical storm intensity and
continued to weaken as it sailed west-southwestward across the Arabian
Sea. A SSM/I pass at 04/1342 UTC depicted only isolated convection
near the LLCC. Another SSM/I pass about 12 hours later revealed
a fully-exposed LLCC with no deep convection. JTWC issued the final
warning (for the second time) on the system at 0600 UTC on the 5th
with the weak center located about 400 nm east-southeast of the "Horn"
of Somalia. The residual LOW continued to drift westward toward the
Somalian coast for another couple of days but showed no signs of
redevelopment.
Near the port town of Cuddalore, where the cyclone made landfall,
all roads leading to the town were rendered impassable. Many trees
were uprooted and numerous homes lost their roofs. Many thousands
of persons were evacuated from low-lying areas in the Indian states
of Tamil Nadu and Andhra Pradesh. Six deaths, mainly drownings,
were reported in association with the storm, and Indian authorities
reported that 43 fishermen were missing at sea. Heavy rains inundated
thousands of acres of rice paddies in the Sirkali and Papanasam areas.
Some of the highest storm-total rainfall amounts reported were:
Colerron - 235 mm, Sirkali - 201 mm, Manalmedu - 168 mm, and
Papanasam - 120 mm.
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SOUTHWEST INDIAN OCEAN (SWI) - South Indian Ocean West of Longitude 90E
Activity for November: 1 tropical depression
The primary sources of information upon which the narrative is based
are the warnings issued by the TCWC on La Reunion Island, associated
with Meteo France, which is the RSMC for the Southwest Indian Ocean
basin. However, cyclones in this region are named by the sub-regional
centres on Mauritius and Madagascar with longitude 55E as the dividing
line between their respective areas. La Reunion only advises these
centres regarding the intensity of tropical systems. References to
sustained winds should be understood as implying a 10-min averaging
period unless otherwise stated. In the accompanying tracks file
some position comparisons have been made with JTWC's positions, and
warnings from JTWC were used as a source of 1-min avg MSW estimates.
Southwest Indian Ocean Tropical Activity for November
-----------------------------------------------------
An increase in convective activity was noted across the South Indian
Ocean in November, perhaps due to an active phase of the Madden-Julian
Oscillation. An area of convection had developed by the 9th several
hundred miles east-southeast of Diego Garcia. A LLCC developed and
JTWC issued a Formation Alert on the system on 11 November and the
first warning on TC-02S at 12/0000 UTC. La Reunion also initiated
bulletins on the system at 0600 UTC, numbering it Tropical Disturbance
02 for the SWI basin. The system, although weak, was tenacious,
remaining on the charts in one form or another until the 20th. The
first JTWC warning located the center about 450 nm east-southeast of
Diego Garcia. Over the next several days the disturbance drifted
somewhat erratically eastward, remaining quasi-stationary for several
hours at times. Eventually the system began to move more to the south
or south-southwest--the final bulletin from La Reunion at 18/1800 UTC
placed the center about 875 nm east-southeast of Diego Garcia.
JTWC issued one warning (12/1200 UTC) estimating the MSW (1-min avg)
at 35 kts, and the concurrent La Reunion warning indicated gales were
occurring in the southwestern quadrant; however, the next JTWC warning
at 13/0000 UTC indicated that the system was rapidly weakening and
that no more warnings would be issued unless re-intensification
occurred. La Reunion treated the disturbance as a tropical depression
from 12/1200 UTC through 13/1200 UTC with maximum 10-min avg winds
near the center estimated at 30 kts, but it was downgraded back to a
tropical disturbance at 1800 UTC and bulletins discontinued. Bulletins
were re-instated 24 hours later when the system appeared to be getting
better organized once more, and the disturbance was re-upgraded to a
tropical depression at 15/0000 UTC for a 12-hour period. However, at
1200 UTC the system was downgraded once more and was carried as just
a tropical disturbance for three more days. JTWC issued several
Formation Alerts on the system between the 15th and 19th but never
issued any more warnings. (Note: A track was provided for this system
in the November cyclone tracks file.)
***********************************************************************
NORTHWEST AUSTRALIA/SOUTHEAST INDIAN OCEAN (AUW) - From 90E to 135E
Activity for November: 1 tropical LOW
The primary sources of information for Australian Region tropical
cyclones are the warnings and bulletins issued by the three TCWCs
at Perth, Darwin, and Brisbane. Information gleaned from JTWC's
warnings is used as a supplement for times when it was impossible to
obtain Australian bulletins and for comparison purposes. References
to sustained winds should be understood as being based on a 10-min
averaging period unless otherwise noted.
Northwest Australia/Southeast Indian Ocean
Tropical Activity for November
------------------------------------------
During late November the monsoon trough was becoming established to
the north and west of Australia. The western region was more active,
and for some days there were several weak monsoonal LOWs in the Indian
Ocean section of the trough. One of these became sufficiently active
for the Perth TCWC to issue Tropical Cyclone Advices for Christmas
Island. At 0700 UTC on 28 November the tropical LOW was located about
60 nm east-southeast of Christmas Island. Over the next couple of
days the system drifted generally in an eastward direction. By
0400 UTC on the 29th the LOW was about 250 nm east of the island and
the final advice was issued. The LOW continued to drift eastward and
by 0400 UTC on 30 November was located about 300 nm east of Christmas
Island. There were indications that the system might be about to
strengthen into a cyclone so a High Seas Gale Warning was issued.
However, by 1000 UTC the LOW appeared to be weakening and the gale
warning was cancelled. (Note: A track was provided for this system
in the November cyclone tracks file.)
A special thanks to Carl Smith, who lives on the Gold Coast of
Queensland, for sending me a report on this tropical LOW from which
some of the above material was taken.
***********************************************************************
NORTHEAST AUSTRALIA/CORAL SEA (AUE) - From 135E to 160E
Activity for November: No tropical cyclones
***********************************************************************
SOUTH PACIFIC (SPA) - South Pacific Ocean East of Longitude 160E
Activity for November: No tropical cyclones
***********************************************************************
EXTRA FEATURE
In order to shorten the amount of typing in preparing the narrative
material, I have been in the habit of freely using abbreviations and
acronyms. I have tried to define most of these with the first usage
in a given summary, but I may have missed one now and then. Most of
these are probably understood by a majority of readers but perhaps a
few aren't clear to some. To remedy this I developed a Glossary of
Abbreviations and Acronyms which I first included in the July, 1998
summary. I don't normally include the Glossary in most months in
order to help keep them from being too long. If anyone would like to
receive a copy of the Glossary, please e-mail me and I'll be happy
to send them a copy.
***********************************************************************
AUTHOR'S NOTE: This summary should be considered a very preliminary
overview of the tropical cyclones that occur in each month. The cyclone
tracks (provided separately) will generally be based upon operational
warnings issued by the various tropical cyclone warning centers. The
information contained therein may differ somewhat from the tracking and
intensity information obtained from a "best-track" file which is based
on a detailed post-seasonal analysis of all available data. Information
on where to find official "best-track" files from the various warning
centers will be passed along from time to time.
The track files are not being sent via e-mail. They can be retrieved
in the following manner:
(a) FTP to: hrd-type42.nhc.noaa.gov [140.90.176.206]
(b) Login as: anonymous
(c) For a password use your e-mail address
(d) Go to "data" subdirectory (Type: cd data)
(e) Set file type to ASCII (Type: ascii)
(f) Transfer file (Type: get remote_file_name local_file_name )
(The files will be named with an obvious nomenclature--using
November as an example: nov00.tracks)
(g) To exit FTP, type: quit
Both the summaries and the track files are standard text files
created in DOS editor. Download to disk and use a viewer such as
Notepad or DOS editor to view the files.
The first summary in this series covered the month of October,
1997. If anyone wishes to retrieve any of the previous summaries,
they may be downloaded from the aforementioned FTP site at HRD. The
summary files are catalogued with the nomenclature: nov00.sum, for
example.
Back issues can also be obtained from the following websites
(courtesy of Michael Bath, Michael V. Padua, Tom Berg, Michael
Pitt, and Rich Henning):
http://australiasevereweather.com/cyclones/>
http://www.typhoon2000.com> OR http://www.geocities.com/taifun00/>
http://www.hurricanealley.net/>
http://www.qisfl.net/home/hurricanemike>
http://www.met.fsu.edu/gsc/Docs/Grads/henning/cyclones/>
Another website where much information about tropical cyclones may
be found is the website for the UK Meteorological Office. Their site
contains a lot of statistical information about tropical cyclones
globally on a monthly basis. The URL is:
http://www.met-office.gov.uk/sec2/sec2cyclone/sec2cyclone.html>
TROPICAL CYCLONE REPORTS AVAILABLE
I have discovered that JTWC now has available on its website the
complete Annual Tropical Cyclone Report (ATCR) for 1999 (1998-1999
season for the Southern Hemisphere). Also, ATCRs for earlier years
are available also.
The URL is: http://199.10.200.33/jtwc.html>
Also, TPC/NHC has available on its webpage nice "technicolor"
tracking charts for the 2000 Atlantic and Eastern North Pacific
tropical cyclones; also, official storm reports for all the 2000
Atlantic and Eastern North Pacific cyclones are now available.
The URL is: http://www.nhc.noaa.gov>
Prepared by: Gary Padgett
E-mail: [email protected]
Phone: 334-222-5327 (nights & weekends) / 850-882-2594 (weekdays)
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